An investigation of beam driven Alfvén instabilities in the DIII-D tokamak

Heidbrink, W. W.; Strait, E. J.; Doyle, E. J.; Sager, G.T.; Snider, R. T.

doi:10.1088/0029-5515/31/9/002

Cited by 295 publications

(210 citation statements)

References 38 publications

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“…1͑b͔͒ are the toroidal Alfvén eigenmodes, TAE. [7][8][9][10] shown in cyan. These modes are weakly damped natural resonant frequencies of the plasma, much like the natural oscillation frequency of a violin string.…”

Section: Physics Of Plasmas 13 056109 ͑2006͒mentioning

confidence: 99%

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

et al. 2006

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A wide variety of fast ion driven instabilities are excited during neutral beam injection ͑NBI͒ in the National Spherical Torus Experiment ͑NSTX͒ ͓Nucl. Fusion 40, 557 ͑2000͔͒ due to the large ratio of fast ion velocity to Alfvén velocity, V fast / V Alfvén , and high fast ion beta. The ratio V fast / V Alfvén in ITER ͓Nucl. Fusion 39, 2137 ͑1999͔͒ and NSTX is comparable. The modes can be divided into three categories: chirping energetic particle modes ͑EPM͒ in the frequency range 0 to 120 kHz, the toroidal Alfvén eigenmodes ͑TAE͒ with a frequency range of 50 kHz to 200 kHz, and the compressional and global Alfvén eigenmodes ͑CAE and GAE, respectively͒ between 300 kHz and the ion cyclotron frequency. Fast ion driven modes are of particular interest because of their potential to cause substantial fast ion losses. In all regimes of NBI heated operation we see transient neutron rate drops, correlated with bursts of TAE or fishbone-like EPMs. The fast ion loss events are predominantly correlated with the EPMs, although losses are also seen with bursts of multiple, large amplitude TAE. The latter is of particular significance for ITER; the transport of fast ions from the expected resonance overlap in phase space of a "sea" of large amplitude TAE is the kind of physics expected in ITER. The internal structure and amplitude of the TAE and EPMs has been measured with quadrature reflectometry and soft x-ray cameras. The TAE bursts have internal amplitudes of ñ / n = 1% and toroidal mode numbers 2 Ͻ n Ͻ 7. The EPMs are core localized, kink-like modes similar to the fishbones in conventional aspect ratio tokamaks. Unlike the fishbones, the EPMs can be present with q͑0͒ Ͼ 1 and can have a toroidal mode number n Ͼ 1. The range of the frequency chirp can be quite large and the resonance can be through a fishbone-like precessional drift resonance, or through a bounce resonance.

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Section: Physics Of Plasmas 13 056109 ͑2006͒mentioning

confidence: 99%

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

et al. 2006

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“…13. Comparison of the damping rates calculated with the modified method of Appendix D (dashed curve) and with the method described in the text, (solid curve), for the pa--rameters given in Fig.…”

Section: Omentioning

confidence: 99%

“…(13). Since it does not entail a double radial derivative of the wave function, we evaluate it without toroidicity corrections as follows:…”

mentioning

confidence: 99%

Continuum damping of low-n toroidicity-induced shear Alfven eigenmodes

Berk¹,

Dam

Guo

et al. 1991

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“…In contrast, in the case of neutral beam injection ͑NBI͒, a "hard" nonlinear regime is observed more often, resulting in bursting amplitude evolution and in rapid frequency sweeping. [9][10][11][12][13] Spontaneous formation of phase space holes and clumps 14 is typical of the NBI-driven scenarios. 9 The holes and clumps in the energetic particle distribution function correspond to resonant particles that are trapped in the field of the wave.…”

Section: Introductionmentioning

confidence: 99%

Effect of dynamical friction on nonlinear energetic particle modes

Lilley¹,

Breǐzman²,

Sharapov³

2010

Physics of Plasmas

106

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A fully nonlinear model is developed for the bump-on-tail instability including the effects of dynamical friction ͑drag͒ and velocity space diffusion on the energetic particles driving the wave. The results show that drag provides a destabilizing effect on the nonlinear evolution of waves. Specifically, in the early nonlinear phase of the instability, the drag facilitates the explosive scenario of the wave evolution, leading to the creation of phase space holes and clumps that move away from the original eigenfrequency. Later in time, the electric field associated with a hole is found to be enhanced by the drag, whereas for a clump it is reduced. This leads to an asymmetry of the frequency evolution between holes and clumps. The combined effect of drag and diffusion produces a diverse range of nonlinear behaviors including hooked frequency chirping, undulating, and steady state regimes. An analytical model is presented, which explains the aforementioned diversity. A continuous production of hole-clump pairs in the absence of collisions is also observed.

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An investigation of beam driven Alfvén instabilities in the DIII-D tokamak

Cited by 295 publications

References 38 publications

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

Continuum damping of low-n toroidicity-induced shear Alfven eigenmodes

Effect of dynamical friction on nonlinear energetic particle modes

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